The climate effect of aviation is significant and expected to increase. Reducing the sector&rsquo;s environmental footprint to contribute to global temperature targets will require not only investments in airframe and engine technologies but also operational strategies such as eco-efficient flight routing, focusing on reducing non-CO₂ effects. The D-KULT project (Demonstrator Climate and Environmentally Friendly Air Transport), funded under the German Federal Aviation Research Programme (LuFo), aims to demonstrate the feasibility of optimising flight trajectories with respect to climate effect. The project addresses a multi-objective optimisation problem in which flight trajectories minimise climate effects while maintaining operational and economic efficiency. Operational constraints such as meteorological hazards, regulatory requirements, airspace and airport capacity need to be incorporated to ensure real-world applicability. This work provides a comprehensive overview of the project, describing new developments and major challenges on implementation pathways and summarizes the key findings.</p> <p>D-KULT developed an end-to-end information chain integrating aviation weather forecasting, flight planning, air traffic control, and climate benefit assessment to enable eco-efficient flight routing for testing purposes. Achieving this complex operational and environmental objective required close collaboration across multiple disciplines and substantial upgrades to the majority of participating components. Novel aviation weather products were generated that estimate the climate sensitivity of emissions under prevailing meteorological conditions. Flight planning tools have been extended to take this information into account in addition to the standard data in the flight planning optimization algorithms. In this way, flight planning tools can calculate emissions and corresponding climate effects along flights, both as part of strategic (pre-departure) and tactical (pre-take-off and in-flight) eco-efficient flight optimisation. Developments within D-KULT were tested through a large-scale national contrail avoidance flight trial campaign, including enhanced satellite-based contrail detection methods and assessment and workflow implications in a high-fidelity simulator environment.</p> <p>Results demonstrate substantial progress toward operational climate-optimised aviation but also highlight remaining challenges, including uncertainties in weather forecast and non-CO₂ climate effects, automation needs along the workflow and increased controller workload in dense airspaces. A key requirement for operational implementation is transparent information of prediction uncertainties, enabling informed decision-making when rerouting for climate benefit. These remaining research of achievable climate benefits. Further evaluation focused on operational integration, examining air traffic control procedures, and development needs form the basis for the planned successor programme to D-KULT.